The present application is a National Stage Application of International Application No. PCT/EP00/02708, filed Mar. 28, 2000. Further, the present application claims priority, under 35 U.S.C. xc2xa7119, of German Patent Application No. 199 14 755.8 filed on Mar. 31, 1999.
1. Field of the Invention
The invention relates to an optical arrangement for symmetrizing the beams from laser diodes.
2. Discussion of Background Information
For the production of high-power laser diode arrangements, a plurality of laser diodes are arranged next to one another in a fixed orientation relative to so-called laser diode bars. Such bars achieve optical output of up to approximately 40W and comprise individual emitters arranged in a row with typical dimensions of the radiating surface from 50 xcexcmxc3x971 xcexcm to 200 xcexcmxc3x971 xcexcm, with the linear arrangement of these emitters always occurring in the direction of their greatest expansion. In order to achieve even greater outputs, such laser diode bars are stacked on top of one another in the direction of the smaller extension of the emitters into laser diode stacks. The emission of these stacks is extremely asymmetrical and has a low radiance due to the non-radiating regions between the individual emitters of a bar and among the bars as compared to the individual emitters.
In order to achieve a symmetrical bundle with the greatest possible radiance as is needed, for example, for material processing or for pumping of solid state lasers, optical systems are necessary that, on the one hand, cause a symmetrizing of the beams as well as a fading-out of the non-radiating regions for the purpose of maintaining the radiance.
Arrangements for symmetrizing laser diode stacks are known, for example, for connection to optical fibers and/or focusing in a focal spot. Here, depending on the requirements with regard to symmetrizing and radiance, different concepts are prior art.
The coupling of a stack is described in DE 195 00 513 C1. Here, it is disadvantageous that the minimum distance between the individual bars is three times the thickness of the collimation lenses, which may obstruct the integration of as great as possible a number of bars for a given height.
While an arrangement according to DE 195 44 488 does allow a scaling to very high outputs by using many bars, the radiance achieved is at least one order of magnitude less than the fiber-coupled laser diode bars, such as those according to DE 44 38 368.
Moreover, an optical arrangement of multiple laser diodes arranged next to one another in a fixed allocation for symmetrizing of beams is known (DE 196 45 150 A1). The symmetrizing arrangement here comprises a cylinder lens rotated around the optical axis, a directional lens for deflecting the radiation beams of the individual laser diodes, a redirection lens for compensating the deflection of the directional lens, and a subsequent collimation lens.
The invention provides for an optical arrangement for symmetrizing the beam of a scaleable number of laser diode bars that comprises micro-optic components that are comparably simple to produce, is accessible to a cost-effective miniaturization, and with which the losses in radiance accompanying the symmetrizing are as small as possible. In particular, an improvement of the radiance should be attained as compared to fiber-coupled laser diode bars.
According to one non-limiting aspect of the invention, there is provided an optical arrangement for symmetrizing beams which includes a plurality of laser diodes arranged next to one another. The plurality of laser diodes emit beams which are asymmetrical relative to a first direction and a second direction. The second direction is perpendicular to the first direction. A microcylinder lens optics is arranged in an inclined manner around an optical axis. The beams emitted by the laser diodes in the first direction are collimated and deflected with different angles and are separated thereby. A direction element is arranged downstream of the microcylinder lens optics. The direction element deflects a beam of each individual laser diode in the second direction, whereby each of these beams is deflected by a different angle in the second direction, in such a way that central points of the individual beams converge at a predetermined distance in the second direction. The direction element deflects a beam of the individual laser diode in the first direction in such a way that each of these beams converges at a predetermined distance in the first direction. A redirection element is arranged at a distance downstream of the direction element. The redirection element compensates for different angles of deflection of the beams which are sent through the direction element in a plane.
The plurality of laser diodes may be arranged at least one of one above the other and on a common plane. The plurality of laser diodes may be arranged in a fixed location. The plurality of laser diodes nay be arranged to form a laser diode stack. The optical axis may correspond to an assigned linear array of laser diodes. The microcylinder lens optics may comprise a plurality of microcylinder lenses. The microcylinder lens optics may have sufficient isoplanacy. The redirection element may compensate for different angles of deflection of the beams which are sent through the direction element in a plane defined by the second direction and the optical axis. The first direction may define an xe2x80x9cyxe2x80x9d axis, the second direction may define an xe2x80x9cxxe2x80x9d axis, and the optical axis defines a xe2x80x9czxe2x80x9d axis. The redirection element may compensate for different angles of deflection of the beams which are sent through the direction element in a plane defined by an x-z plane.
The arrangement may further comprise at least one projection lens arranged between the direction element and the redirection element, whereby the at least one projection lens directs the beams in the second direction to a common focal spot. The arrangement may further comprise at least one optical fiber arranged at the common focal spot. The at least one optical fiber may comprise one of a plurality of optical fibers and a fiber bundle. The microcylinder lens optics may comprise a plurality of microcylinder lenses, at least one of the plurality comprising one of a gradient optical microcylinder lens, a spherical microcylinder lens, an aspherical microcylinder lens, and a Fresnel lens. The microcylinder lens optics may comprise a plurality of microcylinder lenses, each the plurality comprising at least one of a gradient optical microcylinder lens, a spherical microcylinder lens, a aspherical microcylinder lens, and a Fresnel lens. The direction element may comprise at least one of a doublet lens, a biconvex lens, and a planoconvex lens. The direction element may comprise spherical surfaces. The direction element may comprise aspherical surfaces.
The arrangement may further comprise an optical element arranged adjacent the direction element. The optical element may evenly deflect the beams in the second direction in such a way that the beams in first direction are separated from one another at a predetermined distance in the second direction. The optical element may comprise at least one of an array of blazed gratings, a prism stack, and a mirror stack. The optical element may deflect the beams in the second direction by sectioning the direction element and subsequently joining the sections such that they are displaced relative to one another in the second direction. The redirection element may comprise at least one of an array of blazed gratings, a prism stack, and a mirror stack.
The arrangement may further comprise a deflecting element arranged between the direction element and the redirection element. The deflecting element may be arranged adjacent the redirection element, whereby the deflecting element deflects beams in the first direction in such a way that they leave the redirection element parallel to the optical axis. The deflecting element may comprise at least one of an array of blazed gratings, a prism stack, and a mirror stack. The deflecting element may comprise a diffraction element. The redirection element may comprise a diffraction element.
The arrangement may further comprise a lens located between the direction element and the redirection element, whereby the lens causes a collimation of individual beams in the second direction. The lens may be located adjacent the redirection element and may comprise at least one of a doublet lens, a biconvex lens, and a planoconvex lens. The direction element may comprise spherical surfaces. The direction element may comprise aspherical surfaces.
The arrangement may further comprise a focusing lens arranged downstream of the redirection element, whereby the focusing lens focuses the beams into one or more focus spots or points. The focusing lens may comprise at least one of an achromate lens, an achromate and a meniscus lens, a planoconvex lens, a planoconvex lens, a meniscus lens, and a biconvex lens. The focusing lens may comprise a spherical profile form. The focusing lens may comprise an aspherical profile form.
The invention may also provide for an optical arrangement for symmetrizing beams comprising a plurality of laser diodes arranged to form an array. A plurality of microcylinder lenses is arranged adjacent the array. A direction element is arranged downstream of the plurality of microcylinder lenses. The direction element deflects some beams in an xe2x80x9cxxe2x80x9d direction, whereby each of these beams is deflected by a different angle in the xe2x80x9cxxe2x80x9d direction, in such a way that central points of individual beams converge at a predetermined distance in the xe2x80x9cxxe2x80x9d direction. The direction element deflects some beams in a xe2x80x9cyxe2x80x9d direction in such a way that each of these beams converges at a predetermined distance in the xe2x80x9cyxe2x80x9d direction. A redirection element is arranged at a distance downstream the direction element. The redirection element compensates for different angles of deflection of the beams which are sent through the direction element.
The invention can also provide for an optical arrangement for symmetrizing beams comprising a plurality of laser diodes arranged to form an array. A plurality of microcylinder lenses is arranged adjacent the array. A direction element is arranged downstream of the microcylinder lenses. The direction element deflects some beams in a second direction, whereby each of these beams is deflected by a different angle in the second direction, in such a way that central points of individual beams converge at a predetermined distance in the second direction. The direction element deflects some beams in the first direction in such a way that each of these beams converges at a predetermined distance in the first direction. A redirection element is arranged at a distance downstream the direction element. At least one lens is arranged adjacent the redirection element. At least one optical fiber is arranged downstream the redirection element and the at least one lens. At least some of the beams exiting the redirection element are directed to a common focal spot on the at least one optical fiber.
Using a microcylinder lens that is assigned to each individual bar and inclined to its optical axis (z-axis), the beams emitted by the individual emitter of each bar in the direction of the stack of the laser diode bars is collimated, differently deflected, and thus separated. This deflection occurs such that the centers of the beams of individual emitters of different bars lying above one another impact a redirection element at the same height in this direction at a predetermined distance. A direction element located downstream from the microcylinder lenses causes a deflection of the beams of the individual emitters of a bar in the direction of the linear arrangement of the individual emitter such that the beam centers of the emitters of one bar occur at a predetermined distance on the redirection element in this direction. Moreover, the direction element deflects the beam centers of the individual bars in the direction of the stack such that all centers in the stack direction also fall on the redirection element. The redirection element deflects the emission beams originating from the individual emitters such that the deflection angles produced by the direction element are compensated again. A projection lens adjacent to the redirection element projects the beams of each bar in a focal spot, located at a predetermined distance. These focal spots are coupled into the face surfaces positioned there of the spread fibers of an optical fiber bundle. This bundle causes the focal spots, which were originally arranged one above the other in the direction of the stacking of the bars, to be rearranged into the desired symmetrical total focal spot.
By way of the multiple use of the direction and redirection element and the projection lens for all bars, the arrangement thus described allows a simple and cost-effective symmetrizing of the radiation from laser diode stacks while maintaining the radiance of the individual emitters to the greatest extent possible.